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AN ABRIDGMENT 



OF 



SMITH'S 

ILLUSTRATED ASTRONOMY. 



DESIGNED FOR THE USE OF 



JUNIOR CLASSES 



IN THE 



PUBLIC OR COMMON SCHOOLS 



IN THE UNITED STATES. 



By ASA^SMITH, 
PRINCIPAL OF PUBLIC SCHOOL No. 12. 

CITY OF NEW YORK. 



FIFTH EDITION. 

NEW YORK. 
PUBLISHED BY* CADY & BURGLSS, 

60 JOHN STREET. 

1850. 



Entered, according to Act ot Congress, in tht year 1848, 

3y ASA SMITH, 

in the Clerk's Olfice of the District Court of the United States, for the 

Southern District of New- York. 



Vincent L. Dill, Stereotyper, C. A. Alvord, Printer, 

Sun Bunding, Is Y. 






jb 



PREFACE. 



Since the publication of the " Illustrated Astronomy," 
the Author has thought advisable, to make an abridgment of it, 
for the use of the junior classes in our Public and Ward Schools. 
The number of scholars studying Astronomy was considered by 
some too large, to incur the expense of furnishing them all, 
with the illustrated work. It was therefore suggested, that an 
abridgment might be advantageously used by the junior, in con- 
nection with the illustrated work in the senior classes. 

All the questions and answers in the abridgment, are taken 
from the Illustrated Astronomy ; so that when a scholar is pro- 
moted from the junior to the senior class, there will be no disa- 
greement arising from a change of books. In the abridgment, 
a small part of the text is left out ; that part which could not 
well be understood without the diagram before the eye. 

Several of the most important diagrams in the Illustrated 
Astronomy, have been inserted in the abridgment. These 
will be found very acceptable, both to Teachers and Pupils, in 
illustrating the general principles of astronomy, which without 
illustrations, are deprived of much that is pleasing to the eye 
and instructive to the understanding. 

The Author has not inserted in this edition the Glossary and 
the Problems on the Globes; if it should be thought desirable 
by teachers, to have them inserted, they will be added in a 
future edition. 

ASA SMITH, 
Principal of Public School No. 12, 
City of New York 



GEOMETRICAL DEFINITIONS. 

The Teacher should require the Pupils to understand the following Geomet- 
rical definitions, before they are allowed to proceed with the following 
Lessons : — 

What is ? 

A Straight Line is the shortest line that can be drawn between any two points. 

A Surface is that which has length and breadth ; but no thickness. 

A Plane is a straight even surface. The plane of a circle, is the surface contained 
within it, and continued out of it on all sides, indefinitely. The top of a round centre 
table, may be said to represent the plane of a circle. 

Parallel Lines are lines continued in the same direction, and at the same distance from 
each other. They may be either straight or curved lines. 

A Circle is a plane figure, bounded by a curve line, every part of which is equally 
distant from the centre. 

The Diameter of a Circle is a straight line, passing through the centre, and terminating 
both ways by the circumference. 

The Circumference of a Circle is the curve line which bounds it. " 

The Circumference of every Circle is supposed to be divided into 360 equal parts, called 
degrees ; each degree into 60 equal parts, called minutes, and each minute into 60 equal 
parts, called seconds. 

The Radius of a Circle, is a straight line, drawn from the centre to the circumference 

A Quadrant is a quarter of a circle, and contains 90 degrees. 

Jl Semi-circle is the half of a circle, and contains 180 degrees. 

Jin Jingle is formed by one line, meeting another at a point. 

Jl Right Angle is an angle which contains 90 degrees, or a quarter of a circle. 

Jin Acute Angle is an angle which contains less than 90 degrees. 

An Obtuse Angle is an angle which contains more than 90 and less than 180 degrees. 

Parallel or Concentric Circles, are two or more circles drawn around the same centre, 



PARALLEL LINES 




CONCENTRJC CIRCLES 



ABRIDGMENT 



OF 



SMITH'S ILLUSTRATED ASTRONOMY, 



LESSON I. 



Question. What is the body called upon which we live ? 

Answer. It is called the Earth, or World. 

Q. What idea had the Ancients respecting the shape ot 
the earth ? 

A. They believed it was an extensive plain, 
rendered uneven by hills and mountains. 

Q. Why did they think it was an extended plain ? 

A. Because they formed their opinions from 
appearances only. 

Q. Did they believe that the earth had any motion ? 

A. They did not ; they believed that the earth 
rested on a solid, immovable foundation. 

[They very naturally came to this conclusion, as they were entirely ignorant of the 
laws of attraction or gravitation. They believed if the earth were to turn over, that 
every thing would be precipitated from its surface,] 

Q. Had they any definite ideas respecting what held the 
earth up ? 

A. Their views were very vague and unsatis- 
factory. 

[There have been many absurd ideas advanced, at different ages of the world, as to 
what supported the earth. Some supposed it to be shaped like a Canoe, and to float upon 
the waters ; others, that it rested upon the back of an Elephant, or huge Turtle ; 
while, according to mythology, Atlas supported it upon his shoulders : but, what kept 
the waters in their place, or upon what the Elephant, Turtle, or Atlas stood — this was a 
mystery they could never solve.] 



6 ABRIDGMENT OF SMITH'S 

Q. Did they believe the earth extended the same distance in 
all directions ? 

A. They believed it to extend much farther 
from east to west than from north to south. 

[They observed that in going east or west, on the same parallel of latitude, no change 
took place in the appearance of the heavens ; but in going north or south, on the same 
meridian, every sixty miies caused a difference of one degree in the elevation of the 
pole, and in the position of the circles of daily motion of the sun and other heavenly 
bodies j therefore they concluded that the earth was very long from east to west, but 
comparatively narrow from north to south. From this originated the use of the terms 
longitude and latitude j longitude meaning length, and latitude, breadth.] 

Q. What ideas had they respecting the motions of the sun, 
moon, and stars ? 

A. They supposed that they revolved around 
the earth, from east to west, every day. 

Q. What was this system called, that supposed the earth to 
be at rest in the centre, and all the heavenly bodies to revolve 
around it ? 

A. The Ptolemaic* system. 

[Ptolemy asserted, that the sun, moon, planets, and stars revolved around the earth, 
from east to west, every 24 hours ; and to account for their not falling upon the earth, 
when they passed over it, he supposed that they were each fixed in a separate hollow 
crystalline globe, one within the other. Thus the moon was in the first ; Mercury in the 
second ; Venus in the third ; the sun in the fourth ; Mars in the fifth ; Jupiter in the 
sixth: Saturn in the seventh; — (the planet Herschel was not known at this tirne N — the 
fixed stars in the eighth. He supposed the stars to be in one sphere, as they are kept in 
the same positions with respect to each other To permit the light of the stars to pass 
down to the earth, he supposed these spheres or globes were perfectly clear or transpa- 
rent like glass. The power which moved these spheres, he supposed, was communica- 
ted from above the sphere which contained the stars.] 



LESSON II. 

Question. Every one is conscious that the sun, which rises 
daily in the east and sets in the west, is the same body; where 
does it go during the night ? 

Answer. It appears to pass round under the 
earth. 

Q. When we look out upon the stars, on successive evenings, 
they appear to have a definite position with respect to each 
other, and a westward movement, like the sun ; what motion do 
they appear to have from their setting to their rising ? 

A. They appear to pass under the earth. 

* Tole-ina'-ie 



ILLUSTRATED ASTRONOMY. 7 

Q. From the north to the south point of the heavens, there 
is a continuous arc of stars, and in their passage under the 
earth they are not at all disarranged, what can you infer from 
this fact ? 

A. That they pass completely around the earth, 
and every thing attached to it. 

Q. We see no body at rest that does not touch some perma- 
nent support, but we see bodies in motion supported for differ- 
ent lengths of time without resting upon any other surface ; if 
the earth is hung upon nothing, is it probably at rest? 

A. It is more probable that it is in motion. 

Q. If we throw a ball, does the same side always remain 
forward ? 

A. It does not; it turns over continuously. 

Q. What do we call the line round which it turns ? 

A. Its axis. 

Q. If a fly were on the ball, would distant objects appear to 
him to be stationary ? 

A. They would appear to revolve around the 
ball, as often as it turned over. 

Q. If the earth is moving in space, is it in accordance with 
the known motion of ordinary bodies, to suppose that the same 
side remains forward ? 

A. It is not. It is more reasonable to suppose 
that it turns on its axis. 

Q. If the earth turns, and we are carried round on its sur- 
face, what appearance must the sun and distant stars necessa- 
rily present? 

A. They must appear to move around the earth 
in the opposite direction. 



8 



LESSON III. 

Question. What other reason can you give for the earth's 
turning 1 

Answer. The stars are so distant, that their mo- 
tion would be immensely swift, in comparison 
with the motion of the earth, to produce the 
same effect. 

Q. But have we not positive proof, and that too of different 
kinds, that the earth turns on its axis ? 

A. We have. — 1. The shape of the earth, ele- 
vated at the equator and depressed at the poles, 
can be accounted for on no other supposition. 

2. A body at the equator, dropped from a great 
height, fails eastward of the perpendicular. 

3. The trade winds and ocean currents in the 
tropical regions are clearly traceable to the same 
cause. 

Q. If the earth is moving in space, does it proceed in a 
straight line ? 

A. It does not ; but it would do so, were it not 
attracted by other bodies. 

Q. What is the attraction, by which all particles of matter 
tend towards each other, called 1 

A. The attraction of gravitation. 

Q. What large body, by its attraction, causes the earth to 
revolve around it in a curve line ? 

A. The sun. 

Q. What other similar bodies revolve around the sun ? 

A. The planets. 

Q. What may we call the earth, when considered with 
regard to its size, shape, motions, &c. ? 

A. One of the planets. 

Q. What science describes these characteristics of the earth, 
and other heavenly bodies ? 

A. Astronomy. 



ILLUSTRATED ASTRONOMY. 3 

LESSON IV. 

ASTRONOMY. 

Question. What is Astronomy ? 

Answer. Astronomy is the science which treats 
of the heavenly bodies. 

Q. What are the heavenly bodies ? 

A. The sun, moon, planets, comets, and stars. 

Q. Are they all of the same magnitude, or size ? 

A. The sun and stars are much larger than the 
other bodies. 

Q. Are they all at the same distance from the earth ? 

A. They are not; the moon is the nearest, and 
the stars the most distant. 

Q. Do they all emit light of themselves ? 

A. They do not. 

Q. How are they divided in this respect ? 

A. They are divided into two classes, luminous 
and opaque. 

Q. What is a luminous body ? 

A. It is a body which shines by its own light. 

Q. What is an opaque body ? 

A. It is a body which shines only by reflecting 
the light of a luminous body. 

Q. Which are the luminous bodies in the heavens ? 

A. The sun and fixed stars are luminous bodies. 

Q. Which are the opaque bodies in the heavens ? 

A. The moon, planets, and comets. 

Q. Why do the moon, planets, and comets appear luminous ? 

A. Because they reflect to us the light of the 
sun. 

Q. What is the shape of the heavenly bodies ? 

A. They are round like a globe or ball. 

Q. What do the sun, moon, planets, and comets constitute ? 

A. They constitute the solar system. 



10 ABRIDGMENT OF SMITH'S 

LESSON V. 

THE SOLAR SYSTEM. 

Question, How are the bodies constituting the solar system 
arranged ? 

Answer. The sun is placed in the centre of the 
system, with the planets and comets revolving 
around it at unequal distances. 

Q. How many planets are there in the solar system ? 

A Thirty-six is the number known at present. 

Q. How are they divided with respect to their motion ? 

A. They are divided into two classes, primary 
and secondary. 

Q. What is a primary planet ? 

A. It is a planet which revolves around the 
sun only. 

Q. What is a secondary planet? 

A. It is a planet which revolves around its pri 
mary, and with it around the sun. 

Q. What are the secondary planets usually called ? 

A. They are called satellites or moons. 

Q. How many primary planets are there ? 

A. Sixteen ; eight being asteroids or small 
planets. 

Q. What are their names, beginning at the sun ? 

A. Mercury, Venus, the Earth, Mars, (Vesta, 
Astrsea, Juno, Ceres, Pallas, Hebe, Iris, Flora,) 
Jupiter, Saturn, Herschel, or Uranus, and Lever- 
rier, or Neptune. 

Q. How many secondary planets or moons are there ? 

A. Twenty. 

Q. Which planets have moons ? 

A. The Earth has 1, Jupiter 4, Saturn 8, Her- 
schel 6, and Leverrier 1. 



SOLAR SYSTEM 










ILLUSTRATED ASTRONOMY. 11 

Q. In what direction do all the planets revolve on their axes, 
and around the sun ? 

A. From west to east. 

[Note. — In examining the Solar System, an arrangement of 
extraordinary beauty and harmony, presents itself. The Sun, 
which is 500 times larger than all the planets, both primary 
and secondary, combined, occupies the centre, diffusing light 
and heat in all directions. A curious and extraordinary law 
seems to regulate the distances and motions of all the planets. 
The following are some of their peculiarities, viz : — 

1st. The Sun, which occupies the centre, revolves on its axis 
from west to east. 

2d. All the primary planets revolve around the Sun in the 
same direction, from west to east. 

3d. The secondary planets, or moons, revolve around their 
primaries from west to east. 

4th. All the planets, both primary and secondary, revolve on 
their axes from west to east. 

5th. The orbits of all the planets, both primary and second- 
ary, lie nearly in the same plane of the Sun's equator. 

From this it will be seen that all the motions of the planets 
in our solar system are in one direction ; a circumstance which 
clearly demonstrates, that they originated from the same cause, 
and are governed by the same laws. To this remarkable har- 
mony in the movements of our Solar System, there is supposed 
to be one exception, viz., the retrograde motion of the Satellites 
of Uranus. But this fact has not been fully settled by Astrono- 
mers. For a more full description of the origin of the Solar 
System, see Illustrated Astronomy, page 47.] 



12 ABRIDGMENT OF SMITH'S 



LESSON VI. 

Question. How many revolutions has a primary planet? 

Answer. Two ; one on its axis, and another 
around the sun. 

Q. What is the axis of a planet? 

A. It is a straight line, round which it turns. 

Q. What is the path called, in which a planet revolves 
around the sun ? 

A. It is called its orbit. 

Q. What is the plane of the earth's orbit, extended to the 
heavens, called ? 

A. It is called the ecliptic. 
Q. Why is it so called? 

A. Because eclipses take place, only when the 
moon is in its plane. 

Q. How many revolutions has a secondary planet? 

A. Three. 1st, the revolution upon its axis; 
2d, the revolution around its primary; 3d, the 
revolution with its primary around the sun. 

Q. How are the planets divided, with respect to their dis- 
tance from the sun ? 

A. Into inferior and superior, according as their 
distance from the sun is inferior or superior to 
that of the earth. 

Q. Which are the inferior planets? 

A. Mercury and Venus. 

Q. Which are the superior? 

A. Mars, the Asteroids, Jupiter, Saturn, Her- 
schel, and Leverrier. 



ILLUSTRATED ASTRONOMY. 13 

Q. How many kinds of conjunction are there ? 
A. Two ; inferior and superior. 

Q. When is a planet in inferior conjunction with the sun ? 

A. When it is between the earth and sun. 

Q. What Planets can be in inferior conjunction ? 

A. Mercury and Venus ; also the moon. 

Q. When is a planet in superior conjunction ? 

A. When the earth and planet are on opposite 
sides of the sun. 

Q. What planets can be in superior conjunction with the 
Sun? 

A. All the planets except the earth and moon. 

Q. When is a planet in opposition ? 

A. When the earth is between the sun and 
planet. 

Q. What planets can have opposition ? 

A. The superior planets. ♦ 



14 



ABRIDGMENT OF SMITHS 



LESSON VII. 



DIAMETERS. 



Miles. 

Sun, 886,952 

Mercury, 3,200 
Venus, 7,700 

Earth, 7,912 

Mars, 4,189 

Vesta, 270 

Astraea, unknown. 
Juno, 1,400 

Ceres, 1,600 

Pallas,* 2,100 
Hebe, unknown. 
Iris, " 

Flora, " 

Jupiter, 87,000 
Saturn, 79,000 
Herschel, 35,000 
Leverrier^ 35,000 



Magnitudes — 

THE 

Earth being 1 



1,384,472 
1 

17 

9 

TV 

1 

l 
• i 

l 

1 - - - - 2WOl5" 

Unknown. 
i 

TF6" 
__l_ 

' 135 

1 
.T5 

Unknown. 



1,280 

1,000 

80 

8Q 



Distances froivi 
the Sun. 



Miles. 

37,000,000 
68,000,000 
95,000,000 
142,000,000 
225,000,000 
253,000,000 
254,000,000 
263,000,000 
263,000,000 
Unknown. 



485,000,000 

890,000,000 

1,800,000,000 

2,850,000,000 



Revolution 



their axis. 



Days. Hours. 
25 10 
24 
231 
24~ 
241 

Unknown. 



10 
101 



Revoi 


.UTION 


AROUND 


THE 


Sun. 


^ears. 


Days. 




88 




224 


1 





1 


321 


3 


230 


4 


105 


4 


131 


4 


222 



11 

29 

84 

166 



314 

16: 

5 



* Herschel estimated the diameter of each of the asteroids to "be under 200 miles 
Their great distance, extreme smallness, and nebulous appearance, render it extremely 
difficult to ascertain their size with accuracy. 



LESSON VIII. 

CENTRIPETAL AND CENTRIFUGAL FORCE. 

Question. What is that force called with which all bodies 
attract each other in proportion to their mass ? 

Answer. The attraction of gravitation. 

Q. What is centripetal force ? 

A. It is the force which draws a body towards 
the centre round which it is revolving. 

Q. What large body, by its attraction, exerts a centripetal 
force upon all the primary planets and comets ? 

A. The sun. 

Q. What body exerts a centripetal force upon the moon ? 



A. 



The earth. 



ILLUSTRATED ASTRONOMY. 15 

Q. What bodies exert a centripetal force upon tne other 
moons ? 

A. The primary planets around which they 
revolve. 

Q. What is the centrifugal force of a heavenly body ? 

A. It is that force which moves it forward in its 
orbit. 

Q. How do these two forces cause the planets to more ? 

A. They cause them to move in circular or 
elliptical orbits. 

[A body projected by any force would always move forward in a straight line, and 
with the same velocity, unless acted upon by some other force. A ball discharged from 
a gun or thrown from the hand soon loses its projectile force by the resistance of the 
atmosphere, and is brought to the ground by the attraction of the earth, of centripetal 
force. (Fig 3.) These two forces can be well illustrated, (See Fig. 1, 2.) by tying a 
string to a ball and swinging it around ; the centrifugal force imparted to the ball by the 
hand and by means of the string, causes the ball to move in a circle ; but if the string 
should break, the centrifugal force would carry it off in a straight iine, if the ball was 
not attracted by the earth. The string corresponds to the attraction of the sun in our 
solar system, which causes the planets to move in regular curves around the sun. instead 
of straight lines. If the attraction of the sun or centripetal force should cease, the plan- 
ets would fly off into space in straight lines ; but if the centrifugal force should cease, 
and the centripetal force continue, the planets would immediately fall into the sun.] 

Q, What is a circle ? 

A. It is a plane figure bounded by a curve line, 
all parts of which are equally distant from the 
centre. 

Q. What is an ellipse ? 

A. It is an oval figure, represented by an oblique 
view of a circle. 

[Note. — Teachers should be sure that the pupils understand the definition of an ellipse, 
because in viewing some of the diagrams they may receive a wrong impression in the 
diagram representing the seasons, the earth's orbit appears very elliptical : this would 
be well understood by the pupil, should the teacher call his particular attention to it. 
Also, a plane of a circle should be well understood.] 

Q. What are the foci of an ellipse? 

A. They are the two points, around which the 
ellipse is drawn, and are equally distant from the 
centre. 

Q. Where is the sun situated within the orbit of each 
planet ? 

A. It is situated, not in the centre ; but in the 
lower focus. 



16 

Q. What is the shape of the orbits of all the planets ? 

A. Elliptical, or longer one way than the other. 

THE MEAN AND TRUE PLACE OF A PLANET. 

Q. What is the mean place of the earth, or a planet in its 
orbit 1 

A. It is that point in its orbit where it would 
be if it moved in a circle, and with the same 
velocity at all times. 

Q. What is the true place of the earth or a planet ? 

A. It is that point in its orbit where it really is 
at any given time. 

Q. What is the aphelion ? 

A. It is that point in the orbit of the earth or 
planet farthest from the sun. 

Q. When is the earth in the aphelion, or farthest from the 
sun? 

A. July 1st. 

Q. What is the perihelion ? 

A. It is that point in the orbit of the earth or 
planet nearest to the sun. 

Q. When is the earth in the perihelion, or nearest to the 
sun I 

A. January 1st. 






LESSON IX. 

THE SUN. 
Question. What body is the centre of the solar system? 

Answer. The sun. 

Q. Describe the sun ? 

A. The sun is a large luminous body, which 
gives light and heat to the whole solar system. 



A CUT SECTION OF THE SUN 

SHOWING THE SPOTSAUMINOUS ATMOSPHERE,AND THE OPAQUE BODY 
OF THE SUN. 




ILLUSTRATED ASTRONOMY. 17 

Q. What is the diameter of the sun? 

A. 886,952 miles. 

Q. How much larger is the sun than the earth ? 

A. It is 1,384,472 times greater. 

Q. What is the size of the sun compared with the planets ? 

A. It is 500 times as great as the bulk of all the 
planets. 

Q. What can you say of its mass or weight ? 

A. It is about 750 times the mass of all the 
planets. 

Q. What is the distance of the sun from the earth ? 

A. It is about 95,000,000 of miles. 

Q. What did the ancient astronomers consider the sun to be ? 

A. A large globe of fire. 

Q. What do astronomers at the present day consider it to be ? 

A. An opaque body like the earth, surrounded 
by a luminous atmosphere. 

Q. What motions has the sun? 

J.. It has three motions — 1st, on its axis; 2d, 
around the centre of gravity of the solar system; 
3d, around the centre of the universe. 

[The term universe is used by Astronomers, though perhaps improperly, to designate 
the great cluster or firmament of stars in which our sun is situated. This cluster 
includes all the single stars that can be seen with the naked eye, and all those composing 
the galaxy or milky way. The number of stars or suns in the cluster is estimated at 
m#my millions ; all which, like our sun, are supposed to revolve around the common 
centre of gravity of the whole cluster. Several thousand other distinct clusters or nebu- 
lae, situated without our firmament, can be seen by the best telescopes, nearly all of 
which are invisible to the unassisted eye.] 



LESSON X. 

Question, What is the inclination of the sun's axis to that 
of the ecliptic. 

Answer. About 7^ degrees. 

Q. In what time does it revolve on its axis? 

A. In about 25 days and a half. 

2* 



18 

Q. How is the revolution of the sun on its axis determined ? 

A. By spots on its surface, which first appear 
on the east side, pass over, and disappear on the 
west side. 

Q. What is the nature of these spots? 

A. They are supposed to be openings in the 
luminous atmosphere, which enable us to see the 
dark body of the sun. 

Q. What occasions these openings in the luminous atmos- 
phere ? 

A. They have been attributed to storms and 
various other causes. 

Q. Do these spots undergo any changes ? 

A. They are constantly changing, and some- 
times very rapidly. Some have appeared, others 
disappeared suddenly. 

Q. On what part of the sun do they appear ? 

■A. Within about thirty degrees of its equator. 

Q. Is the surface of the sun, in the region of the spots, tran- 
quil or agitated ? 

A. It is in a state of continual and violent agi- 
tation. 



ILLUSTRATED ASTRONOMY. 19 

LESSON XI. 

ECLIPTIC AND ZODIAC. 

Question. What is the ecliptic J . 

Answer. It is the plane of the earth's orbit, 
extended to the heavens, and intersects the equi- 
noctial at an angle of 23i degrees, (23° 28') 

[Note. — It is the apparent path of the sun around the heavens once a year, caused by 
the real motion of the earth around the sun.] 

Q. What is the equinoctial 1 

A. It is a great circle in the heavens directly 
over the equator. 

[Note.— It is the plane of the earth's equator extended to the heavens.] 

Q. What is the zodiac ? 

A. It is a circular belt in the heavens, 16 
degrees wide; 8 degrees on each side of the 
ecliptic. 

Q. What great circle is in the middle of the zodiac ? 

A. The ecliptic or orbit of the earth. 

Q. How is the zodiac divided ? 

A. It is divided into twelve equal parts, called 
signs or constellations of the zodiac. 

Q. How is the ecliptic divided ? 

A. It is divided into twelve equal parts, called 
signs. 

Q. How is each sign divided ? 

A. Each sign is divided into 30 degrees, each 
degree into 60 minutes, each minute into 60 
seconds, &c. 

Q. What are the names of the constellations of the zodiac 
and the signs of the ecliptic ? 

A. Aries, Taurus, Gemini, Cancer, Leo, Virgo, 
Libra, Scorpio, Sagittarius, Capricornus, Aqua- 
rius, and Pisces. 



2U ABRIDGMENT OF SMITH'S 






Q. Do the constellations of the zodiac, and the signs of the 
ecliptic, occupy the same places in the heavens ? 

A. They do not : the signs in the ecliptic have 
fallen back of the constellations about 31 de- 
grees. 

Q. Did the constellations of the zodiac and the signs of the 
ecliptic ever correspond ? 

A. They corresponded to each other about 22 
centuries ago. 

Q. What is the cause of the falling back of the signs of the 
ecliptic among the constellations ? 

A. It is caused by the retrograde motion of the 
equinoxes. 

[Note. — This variation is caused by the pole of the earth varying a little every year. 
This motion of the pole of the earth is similar to that sometimes shown by a top, as it 
spins around on the point. The stem of the top will have a circular motion, describing a 
cone with the apex or top down. This circular motion of the pole of the earth is very 
slow, varying only 50" every year, and requires 25,S68 years to complete a revolution — 
which is called the Platonic or great year. The pole of. the earth is increasing its dis 
tance from the north star, and in 12,900 years it will be about 47° from it ; and when the 
north star is on the meridian, it will be in the zenith of the northern part of the United 
States: but in -25,800 years the pole will have made a complete revolution — so that it 
will point again to the north star.] 

Q. Upon what does the length of the year depend? 

A. It depends upon the revolution of the earth 
from one equinox to the same again. 

Q. Does the earth revolve around the sun in exactly the 
same time that it moves from one equinox to the same equinox 
again ? 

A. It mores from either equinox to the same 
again, seventeen minutes sooner, than around 
the sun. 



ILLUSTRATED ASTRONOMY. 21 



LESSON XII, 



Question. Does the sun appear to move in the heavens 
among the stars ? 

Answer. It has an apparent motion in the eclip- 
tic, eastward around the heavens, during the 
year. 

Q. How is this appearance caused, as the sun is in the cen- 
tre, and does not move ? 

A. It is caused by the earth's moving around 
the sun. 

Q. If the earth is in the sign Aries, where does the sun 
appear to be ? 

A. It appears to be in the opposite sign, Libra. 

Q. As the earth moves round in the ecliptic, where does the 
sun appear to move? 

A. It appears to move in the opposite part of 
the heavens from west to east. 

Q. Which sign does the sun enter, when the north pole 
leans exactly towards the sun ? 

A. Cancer. (21st June.) 

Q. Which sign does the earth enter at this time ? 
A. Capricornus. 

Q. Which signs does the sun enter, when the north pole 
leans sideways to the sun ? 

A. Aries and Libra. 

Q. Which sign does the sun enter, when the north pole leans 
exactly from the sun ? 

A. Capricornus. (22d December.) 

Q. Which are the equinoctial signs ? 

A. Aries, 21st of March — Libra, 23d of Sep- 
tember. 

Q. Which are the solstitial signs ? 

A. Cancer, 21st of June — Capricornus, 22d of 
December. 



22 ABRIDGMENT OF SMITH'S 



LESSON XIII. 

Question. How are the signs of the ecliptic divided ? 

Answer. They are divided into four divisions, 
corresponding to the seasons. 

Q. Which are the spring signs ? 

A. Aries, Taurus, Gemini. 

Q. Which are the summer signs ? 

A. Cancer, Leo, Virgo. 

Q. Which are the autumnal signs ? 

A. Libra, Scorpio, Sagittarius. 

Q. Which are the winter signs ? 

A. Capricornus, Aquarius, Pisces. 

Q. In what time do the equinoxes fall back through the 
whole circle of the Zodiac? 

A. 25,800 years. 

Q. What is this time called ? 

A. The Platonic, or great year. 

Q. How is this motion caused ? 

A. It is caused by a slow annual change in the 
direction of the earth's axis. 

Q. What is longitude in the heavens ? 

A. It is the distance from the first degree of 
the sign Aries, reckoned eastward on the eclip- 
tic, the whole circumference of the heavens. 

Q. When the sun enters Aries, what is its longitude ? 

A. It has no longitude. 

Q. What is the longitude of the earth at that time ? 

A. ISO degrees. 

Q. When the Sun enters Cancer, what is its longitude ? 

A. 90 degrees — the earth's longitude at the 
same time 270 degrees. 

Q. When the sun enters Libra, what is its longitude ? 

A. 180 degrees — the earth's longitude de- 
grees. 






ILLUSTRATED ASTRONOMY. 23 

Q. When the Sun enters Capricornus, what is the longi- 
tude ? 

A. 270 degrees — the earth's longitude at the 
same time 90 degrees. 



LESSON XIV. 

MERCURY. 

Question. Which planet is the smallest and nearest the sun ? 

Answer. Mercury. 

Q. What is the diameter of Mercury ? 

A. 3,200 miles. 

Q. What is its distance from the sun ? 
A. 37 millions of miles. 

Q. What is its magnitude, compared with the earth ? 

A. It is it of the earth's magnitude. 

Q. In what time does it revolve on its axis, or perform its 
daily revolution ? 

A. In about 24 hours. (24 hours 5 minutes.) 

Q. In what time does it revolve around the sun ? 

A. In about 88 days. (87d. 23h. 14m. 33s.) 

Q. How fast does it move in its orbit around the sun ? 
A. It moves 112,000 miles an hour. 

Q. What is the light or heat at Mercury compared with that 
of the earth? 

A. It is about seven times as great. 

Q. What is elongation ? 

A. It is the apparent distance of any planet 
from the sun. 

Q. What is the greatest elongation of Mercury ? 

A. 30 degrees; which may be either east or 
west of the sun. 

Q. Why is Mercury never seen in superior conjunction ? 

A. Because it is so much involved in the light 
of the sun. 



'24 . ABRIDGMENT OF SMITH'S 

Q. Does Mercury experience any change of seasons? 

A. It does not, because its axis is perpendicular 
to its orbit. This causes the sun to be continu- 
ally vertical at the equator. 



LESSON XV. 

VENUS. 
Question. What planet is next to Mercury ? 

Answer. Venus. 

Q. What is the diameter of Venus ? 

A. 7,700 miles. 

Q. What is its distance from the sun ? 

A. 68 millions of miles. 

Q. What is its magnitude compared with the earth ? 

A. It is about n> of the earth's magnitude. 

Q. In what time does it revolve on its axis ? 

A. In about 23^ hours. (23h. 21m.) 

Q. In what time does it revolve around the sun ? 

A. In 224 days. (224d. 16h. 41m. 27s.) 

Q. How fast does it move in its orbit around the sun ? 

A. It moves 75,000 miles an hour. 

Q. What is the comparative light or heat at Venus ? 

A. It is about double that of the earth. 

Q. What is the greatest elongation of Venus ? 

A. About 47 degrees. 

Q. When is Venus a morning star ? 

A. When it is west of the sun, and rises be- 
fore it. 

Q. When is it an evening star ? 

A. When it is east of the sun, and sets after it. 

Q. How long is Venus a morning or an evening star, alter- 
nately ? 

A. About 290 days. 



ILLUSTRATED ASTRONOMY. 25 

Q. Why is Venus a mcrning or an evening star 66 days 
longer than the time of its revolution around the sun ? 

ji. Because the earth is moving around the sun 
the same way. 



LESSON XVI. 

Question. How much is the axis of Venus inclined to that of 
its orbit? 

Answer 75 degrees. 

Q. When the north pole of Venus inclines directly towards 
the sun, how many degrees will the axis point above the sun ? 

A. Only 15 degrees. 

Q. How wide a torrid zone does this make ? 

A. 150 degrees — 75 degrees on each side of the 
equator. 

Q. The tropics are within how many degrees of the poles ? 

A. Within 15 degrees. 

Q. The polar circles are within how many degrees of the 
equator ? 

A. 15 degrees. 

Q. What is the diameter of the polar circles? 

A. 150 degrees. 

Q. Has Venus any variation of seasons ? 

A. She has two summers and two winters at 
the equator, and a summer and winter at each 
of the poles, during the year. 

Q. How does Venus appear, when viewed with a telescope ? 

A. She exhibits phases similar to those of the 
moon. 

Q. What is the transit of a heavenly body ? 

A. It is its passage across the meridian. 

Q, What is meant by the transit of Mercury and Venus ? 

A. It is their passage across the sui/s disc 

3 



26 ABRIDGMENT OF SMITH'S 

Q. What is the disc of the sun or a planet ? 

A. It is the circular illuminated surface visible 
to us. 

Q. How do Mercury and Venus appear, when passing across 
the sun's disc ? 

A. They appear like black spots moving across 
the sun. 

Q. What proof have we that Mercury and Venus are not 
luminous bodies ? 

A. When viewed with the telescope, they 
appear horned like the moon. 

Q. On which side of the sun does the transit begin ? 

A. On the east side, and terminates on the west 
siue. 

Q. What apparent motions have the planets ? 

A. Three ; direct, stationary, and retrograde. 

Q. When does a planet's motion appear to be direct ? 

A. When it appears to move from west t(f east 
among the stars. 

Q. When is a planet's motion said to be stationary? 

A. When it is moving directly towards or from 
the earth. 

Q. When is a planet's motion said to be retrograde ? 

A. When it appears to move backwards, or 
from east to west among the stars. 

LESSON XVII. 

EARTH, DEFINITIONS, &c. 
Question. What is the shape of the earth ? 

Answer. It is round like a globe or ball, a little 
flattened at the poles. 

Q. How do we know the earth to be round ? 

J.. 1st. Navigators have sailed round it, by a 
continued westerly or easterly course. 2d. The 
top-mast of a ship coming in from the sea, always 



ILLUSTRATED ASTRONOMY. 27 

appears first. 3d. The earth's shadow upon the 
moon, in a lunar eclipse, is circular. 

Q. In what manner do the inhabitants stand upon the earth ? 

A. They stand with their feet directed towards 
the centre of the earth. 

Q. What do you understand by the terms upward and down- 
ward ? 

A. Upward is from the centre of the earth, 
downward is towards the centre of the earth. 

Q. What keeps the inhabitants, &c, upon the surface of the 
earth ? 

A. The attraction of the earth. 

Q. What is the axis of the earth ? 

A. It is the straight line round which it per- 
forms its daily revolution. 

Q. What are the poles of the earth ? 

A. They are the extremities of its axis. 

Q. How are the circles of the globes divided? 

A. They are divided into great and small. 

Q. What is a great circle ? 

A. It is a circle whose plane divides the earth 
into two equal parts, called hemispheres. 

Q. What are the poles of a great circle ? 

A. They are two opposite points in the heavens, 
equally distant from all parts of the circumference. 

[Nqte. — The poles of the horizon are the Zenith and Nadir. The poles of 
the equator, or equinoctial, are those points where the earth's axis, if produ- 
ced each way, would meet the heavens. The north star is situated in one of 
these points.] 

Q. What is a small circle ? 

A. It is a circle whose plane divides the earth 
into two unequal parts. 

Q. Which are the great circles, used in Astronomy? 

A. Equator, Meridian, Horizon, Ecliptic, and 
Equinoctial. 

[Note. — The equator divides the earth into northern and southern hemis- 
pheres—the meridian divides it into eastern and western hemispheres, and 
the horizon divides it into upper and lower hemispheres, j 



28 

Q. Which are the small circles, used in astronomy ? 

A. The tropics and polar circles, parallels of 
latitude, altitude and declination. 

[Note.— Parallels of latitude, are small circles parallel to the equator — paral- 
lels of altitude, are small circles parallel to the horizon — parallels of declina- 
tion are small circles on the celestial globe, parallel to the equinoctial, and cor- 
respond to parallels of latitude on the earth ; or if parallels of latitude on the 
earth should be extended to the heavens, they would then become parallels of 
declination.] 

Q. What is the equator ? 

A. It is a great circle, whose plane divides the 
earth into northern and southern hemispheres. 

Q. To what is the plane of the equator perpendicular? 

A. It is perpendicular to the earth's axis, and 
equi-distant from the poles. 

Q. What is the meridian of a place on the earth ? 

A. It is a great circle passing through the place, 
and the poles of the earth 

Q. Into what does the plane of the meridian divide the earth? 

A. Into eastern and western hemispheres. 

Q. What is the latitude of a place on the earth? 

A. It is its distance from the equator, north or 
south. 

Q. On what is it measured ? 
A. On a meridian. 

Q. How far is latitude reckoned ? 

A. Ninety degrees. 

Q. What places have 90 degrees of latitude ? 

A. The poles. 

Q. What are the tropics ? 

A. They are two small circles parallel to the 
equator at a distance of 23^ degrees north and 
south of it. 

Q. What are the polar circles ? 

A. They are two small circles, one around each 
pole, at a distance of 23h degrees from it. 



: 



ILLUSTRATED ASTRONOMY. 29 



LESSON XVIII. 

Question. Which is the first meridian ? 

Answer. It is the meridian from which longitude 
is reckoned. 

Q. Which meridian is generally used in this country as the 
first meridian. 

A. The meridian of London. 

Q. What is the longitude of a place on the earth ? 

A. It is its distance east or west of the first 
meridian. 

Q, How far is terrestrial longitude reckoned ? 

A. It is reckoned 180 degrees, or half round the 
earth. 

Q. What is the horizon ? 

A. It is a great circle which separates the visi- 
ble heavens from the invisible. 

Q. What are the cardinal points of the horizon? 

A. North, East, South, and West. 

Q. How many horizons are there ? 

A. Two; the visible and the rational. 

Q. What is the visible or sensible horizon ? 

A. It is that circle where the earth and sky 
appear to meet. 

Q. What is the rational horizon ? 

A. It is a great circle, parallel to the visible 
horizon, whose plane passes through the centre 
of the earth. 

Q. Into what does it divide the earth ? 

A. Into upper and lower hemispheres. 

Q. Is the rational horizon above or below the visible 
horizon ? 

A. It is below the visible horizon. 



30 ABRIDGMENT OF SMITHES 

LESSON XIX. 
Question. Do all places on the earth have the same horizon ? 

Answer. They do not ; if we change our place 
on the earth, the horizon changes. 

Q. What are the cardinal points in the heavens or the poles 
of the horizon? 

A. The zenith and nadir. 

«Q. What is the zenith ? 

A. It is that point in the heavens directly over 
our heads. 

Q. Do all places have the same zenith ? 

A. They do not; every place has a different 
zenith. 

Q. What is the nadir? 

A. It is that point in the heavens which is oppo- 
site to the zenith, or directly under our feet. 

Q. Are the zenith and nadir fixed points in the heavens ? 

A. They are not ; they make a complete revo- 
lution in the heavens every 24 hours. 

Q. What is the altitude of a heavenly body ? 

A. It is its height or distance from the horizon. 

Q. What is the polar distance of a heavenly body ? 

A. It is its distance from the pole. 

Q. Who are the antipodes ? 

A. Those who live on directly opposite sides of 
the earth. 

Q. Who are the antoeci ? 

A. Those who live in equal latitude, on directly 
jpposite sides of the equator. 

Q. Who are the perioeci ? 

A. Those who live in equal latitude, on opposite 
sides of the pole. 



ILLUSTRATED ASTRONOMY. 31 

LESSON XX. 

EARTH AND SEASONS. 
Question. What is the shape of the earth? 

Answer. It is round like a globe or ball, a little 
flattened at the poles. 

Q. What is its position in the solar system ? 

A. It is the third planet from the sun. 

Q. What is the mean diameter of the earth ? 

A. 7,912 miles. (Equatorial diameter 7,926 

miles ; polar diameter 7,899 miles.) 

Q. How much greater is the equatorial than the polar 
diameter ? 

A. About 27 miles. 

Q. What causes the equatorial diameter to be greater than 
the polar 1 

A. It is caused by the revolution of the earth 
on its axis. 

[As the greater portion of the surface of the earth is covered 
with water; and as the earth revolves on its axis; the water 
recedes from the poles towards the equator, until its tendency to 
run back towards the poles, just balances the effects of the cen- 
trifugal force. This causes the equatorial diameter to be greater 
than the polar. If the earth should stop revolving on its axis, 
the water at the equator would settle away towards the poles, 
until the earth had assumed the form of a globe as near as pos- 
sible. Thus large portions of land in the torrid zone, which 
are now covered by the ocean, would be left dry, and new con- 
tinents and islands would be formed.] 

Q. What is the mean distance of the earth from the sun? 

A. About 95,000,000 of miles. 

[The mean distance of a planet, is the distance it would 
always be from the sun, if its orbit should be reduced to a true 
circle.] 

Q. What is the specific gravity of the earth ? 

A. It is 5^ times the weight of water. (5.48.^ 



32 ABRIDGMENT OF SMITH'S 

Q. In what time does the earth revolve on its axis, or per- 
form its diurnal revolution ? 

A. In 24 hours. (In 23 hours 56 minutes ; as 
seen from the stars.) 

Q. Which way does it revolve ? 

A. From west to east. 

Q. What causes day and night ? 

A. The light of the sun causes day, and the 

shade of the earth causes night. 

Q. How great a portion of the earth is continually in the 
light of the sun ? 

A. One half; the other half being in the shade 

of the earth. 

Q. What does the revolution of the earth upon its axis 
cause ? 

A. The succession of day and night. 



LESSON XXI. 

Question. As the earth turns upon its axis, what effect is pi*o- 
duced ? 

Answer. The sun is continually rising to places 
in the west, and continually setting to places in 
the east. 

Q. In what time does the earth revolve around the sun, or 
perform its annual revolution ? ^ 

A. In 365 days 6 hours. 

Q. How fast does it move in its orbit around the sun ? 

A. 68,000 miles an hour. 

Q. How are the changes of the seasons caused ? 

A. They are caused by the earth's axis being 
inclined to that of its orbit, and its revolution 
around the sun. 

Q. How many degrees is the earth's axis inclined to that of 
its orbit ? 

A. Twenty-three degrees and a half. (23° 28'.) 



. 



ILLUSTRATED ASTRONOMY. '33 

Q. Is the direction of the earth's axis changed during the 
year? 

A. Its change is so slight that it may be consi- 
dered as pointing to the same place in the 
heavens. 

Q. When does the north pole lean directly towards the sun ? 

A. On the 21st of June, called the summer sol- 
stice. 

Q. How many degrees does it lean towards the sun ? 

A. 23h degrees; and the sun is vertical 23! 
degrees north of the equator. 

Q. What seasons does this produce ? 

A. Summer in the northern hemisphere, and 
winter in the southern. 

Q. When does the north pole lean directly from the sun ? 

A. On the 22d of December, called the winter 

solstice. 

Q. When the north pole leans from the sun, what are the 
seasons ? 

A. Winter in the northern hemisphere, and 
summer in the southern. 

LESSON XXII. 
Question. What are the cardinal points of the ecliptic ? 

Answer. The equinoctial and solsticial points. 
Q. At what points of the ecliptic is the earth at the time of 
the solstices ? 

A. At the solstitial points. 

Q. Through how much of its orbit does the earth pass, in 
moving from one solstitial point to the other? 

A. One half of its orbit, or from one side of the 
sun to the other. 

Q. What are those two points called, half way between the 
solstitial points ? 

A. The equinoctial points. 

Q. Why are they so called 1 

A. Because, when the earth is in these points, 



34 ABRIDGMENT OF SMITH'S 

the sun is vertical at the equator, and the days 
and nights are every where equal. 

Q. When is the sun at the vernal equinox ? 

A. On the 21st of March. 

Q. When is it at the autumnal equinox ? 

A. On the 23d of September. 

Q. Which way does the pole lean when the earth is at the 
equinoctial points ? 

A. It leans sideways to the sun, the sun being 
vertical at the equator. 

Q. When the north pole leans towards the sun, why is sum- 
mer produced in the northern hemisphere ? 

A. Because the rays of the sun strike it more 
directly, than in winter ; consequently, they are 
not spread over so great a surface. 

Q. When the north pole leans from the sun, why is winter 
produced in the northern hemisphere 1 

A. Because the rays of the sun strike it so 
obliquely, that they spread over a greater sur- 
face than in summer. 

Q. At what points do the ecliptic and equinoctial intersect 
each other ? 
A. At the equinoctial points. 

Q. At what angle do the ecliptic and equinoctial intersect 
each other ? 

A. 23^ degrees. 

Q. How far are the solsticial points from the equinoctial points ? 

A. Ninety degrees. 

LESSON XXIII. 

MARS. 

Question. What is Mars ? 

Answer. Mars is the fourth planet from the sun. 

Q. What can you say of its size ? 

A. It is the smallest, except Mercury and the 
a'steroids. 



ILLUSTRATED ASTRONOMY. 35 

Q. What is its diameter? 

A. 4,189 miles. 

Q. What is its distance from the sun ? 

A. 142 millions of miles. 

Q. What is its magnitude ? 

A. It is about one seventh of the size of the 
earth. 

Q. In what time does it revolve on its axis ? 

A. In about 24i hours. (24h. 39m. 22s.) 

Q. In what time does it revolve around the sun ? 

A. In one year, 321 days. 

Q. How fast does it move in its orbit ? 

A. 55,000 miles an hour. 

Q. How many degrees does the axis of Mars lean towards 
its orbit ? 

A. About 30 degrees, (30° IS'.) 

Q. Does Mars have any change of seasons ? 

A. The seasons are similar to those of the earth, 
but nearly twice as lonp:. 

J o 

Q. Why are they longer 1 

A. Because Mars is nearly two of our years in 

revolving around the sun. 

Q. What, is the appearance of Mars when seen with the 
naked eye ? 

A. It appears of a red fiery color. 



LESSON XXIV. 

Question. How does Mars appear, when viewed with a 
telescope ? 

Answer. Outlines of apparent continents and 
seas are distinctly seen. 

Q. What appearance have the continents ? 

A. They have a ruddy color, arising proba^ 1 / 
from the nature of the soil. 



36 ABRIDGMENT OF SMITH'S 

Q. Of what color are the seas ? 

A. They appear of a greenish color, caused no 
doubt by contrast with the red color of the con- 
tinents. 

Q. Does Mars present different phases ? 

A. It sometimes appears gibbous. 

Q. When does a planet appear gibbous ? 

A. When we can see more than half, but not 
the whole, of the illuminated surface. 

Q. Does Mars ever appear horned like the moon? 

A. It does not, because it does not pass between 
us and the sun. 

Q. What other appearances does Mars exhibit when viewed 
with a telescope ? 

A. Bright spots are seen alternately at the 
poles. 

Q. When do these spots appear ? 

A. When it is winter, or continual night at the 
poles. 

Q. What is supposed to be the cause of these spots? 

A. Snow and ice, which has accumulated at 
the poles during winter. 

Q. Do these spots continue through the year ? 

A. They entirely disappear as the summer 
advances upon the poles. 

Q. What amount of light and heat has Mars ? 

A. It has about half as much as the earth. 




ILLUSTRATED ASTRONOMY. 37 

LESSON XXV. 

JUPITER. 

Question. What is Jupiter ? 

Answer. Jupiter is the largest planet in the 
solar system. 

Q. How many times larger is Jupiter than the earth ? 

A. It is 1,280 times greater. 

Q. How far is Jupiter from the sun ? 

A. 485 millions of miles. 

Q. What is its diameter ? 

A. 87,000 miles. 

Q. Which diameter is the greater, the polar or equatorial ? 

• A. The equatorial diameter is 6,000 miles 

greater than the polar. 

Q. What causes the equatorial diameter so much to exceed 
the polar? 

A. The quick rotation of the planet on its 
axis. 

Q. In what time does it revolve upon its axis ? 

A. In about 10 hours. (9h. 55m. 50s.) 

Q. In what time does it revolve around the sun ? 

A. In eleven years, 314 days. 

Q. How fast does it move in its orbit around the sun ? 

A. 30,000 miles an hour. 

Q. How many moons has Jupiter ? 

A. Four. 

Q. Has Jupiter any change of seasons ? 
A. It has no change of seasons. 
Q. Why do its seasons not change ? 

A. Because its axis is nearly perpendicular to 
the plane of its orbit,, which causes the sun to be 
always vertical at the equator. 

Q. How does Jupiter appear, when viewed with a telescope ? 

A. Light and dark belts appear to surround it 

4 



38 ABRIDGMENT OF SMITH'S 

Q. What are the light belts ? 

A. They are supposed to be clouds, which are 
thrown into parallel lines by the quick rotation 
of the planet upon its axis. 

Q. What are the dark belts ? 

A. They are probably the body of the planet, 
seen between the clouds. 

Q. Do these belts always appear the same ? 

A. They change frequently, and sometimes the 

clouds break to pieces. 

Q. What is the velocity of its equatorial parts, in turning on 
its axis ? 

A. 25,000 miles an hour. 

Q. What amount of light and heat has Jupiter? 

A. It has 27 times less than the earth. 



LESSON XXVI. 

SATURN. 
Question. What is Saturn ? 

Answer. It is the largest planet except Jupiter. 

Q. What is its magnitude compared with the earth ? 

A. It is about 1,000 times larger. 
Q. What is the diameter of Saturn ? 

A. 79,000 miles. 

Q. What is its distance from the sun ? 

A. 890 millions of miles. 

Q. In what time does it revolve on its axis ? 

A. In about 10£ hours. (lOh. 29m. 16s.) 

Q. In what time does it revolve around the sun ? 

A. In 29 years and a half. (29y. 167d.) 

Q. How fast does it move in its ovbit around the sun ? 

A. 22,000 miles an hour. 

Q. Is there any change of seasons at Saturn ? 

A. There is ; but it is very slow, as it taVos 



ILLUSTRATED ASTRONOMY. 39 

nearly thirty of our years, to complete a year at 
Saturn. 

Q. How much does the axis of Saturn lean-to wards its orbit? 

A. About 30 degrees. (28° 40'.) 

Q. How long is it day and night alternately at the poles ? 
A. About 15 of our years. 

Q. What has Saturn which surrounds it ? 

A. Two large rings of solid matter like the 
planet. 

Q. What is their position around the planet? 

A. They are directly over the equator. 



LESSON XXVII. 

Question. Do these rings revolve with the planet ? 

Answer. They do, and in nearly the same time 
as the planet. 

Q. Are these rings connected with the planet, or separate? 

A. They are separate from the planet, and from 
each other. 

Q. What is the distance from the planet to the inner ring ? 

A. 19,000 miles. 

Q. How wide is the inner ring ? 

A. 17,000 miles. 

Q. How wide is the space between the rings ? 

A. About .1,800 miles. 

Q. What is the width of the outer ring ? 

A. 10,000 miles. 

Q. How thick are these rings ? 

A. About 100 miles. (Some say 1,000 miles.) 

Q. Are these rings uniform ? 

A. They are rough and uneven. 

Q. How many satellites or moons has Saturn ? 

A. Eight. 



40 ABRIDGMENT OF SMITH'S 

Q. What is the position of their orbits ? 

A. Their orbits, excepting one, are directly 
over the rings. 

Q. Does the sun always shine on the same side of the rings? 

A. It shines upon each side alternately for fif 
teen years. 

Q. What amount of light and heat has Saturn ? 

A. It has 90 times less than the earth. 

Q. What appearance has the disc of Saturn ? 

A. It has dark belts similar to those of Jupiter. 



LESSON XXVIII. 

HERSCHEL, OR URANUS. 
Question. When was Herschel, or Uranus, discovered ? 

Answer. In 1781. 

Q. By whom ? 

A. By Sir William Herschel, who was a cele 
brated English Astronomer. 

Q. In what part of the solar system is Herschel situated ? 

A. It is the fifteenth planet from the sun, and 
next to the farthest discovered. 

Q. What is its magnitude ? 

A. It is 80 times larger than the earth. 

Q. What is its distance from the sun ? 

A. 1800 millions of miles. 

Q. In what time does it revolve on its axis ? 

A. It is not certainly known. [It has been 
stated at 1 day 18 hours, but there seems to be 
no proof of it. — Professor Nichol."] 

Q. In what time does it revolve around the sun ? 

A. In about 84 years. (84y. 6d.) 

Q. How fast does it move in its orbit around the sun ? 

A. 15,000 miles an hour. 



ILLUSTRATED ASTRONOMY. 41 

Q. How will the light and heat at Herschel compare with 
the same at the earth ? 

A. They are 368 times less. 

Q. How many moons has Herschel ? 

A. Six moons were seen by Sir Wm. Herschel, 
but only three have been seen by other astrono- 
mers. 

Q. In what direction do these moons move in their orbits ? 

A. They move from east to west, contrary .to 
the motions of all the other planets, both primary 
and secondary. 



LESSON XXIX. 

LEVERRIER, OR NEPTUNE. 

Question. When was Neptune discovered ? 

Answer. In 1846, by Dr. Galle, of Berlin. 

Q. Who published the elements of this planet, and directed 
astronomers to the point in the heavens where, it might be dis- 
covered ? 

A. Leverrier, a celebrated French mathema- 
tician. 

Q. How near the point, where he directed astronomers to 
look, was it found ? 

A. Within one degree. 

Q. What is the diameter of this planet ? 

A. It is about 35,000 miles. 

Q. What is its magnitude ? 

A. It is about 80 times larger than the earth. 

Q. What is its distance from the sun ? 

A. About 2,850 millions of miles. 

Q. In what time does it revolve on its axis ? 

A. It is not known. 

Q. In what time does it revolve around the sun ? 

A. In about 166 years. 



42 ABRIDGMENT OF SMITH'S 

Q. How many moons has Leverrier ? 

A. One ; and another is supposed to have been 
seen. 

Q. What amount of light and heat has this planet ? 

A. About 900 times less than that of the earth. 

Q. Are the primary planets inhabited ? 

A. They appear to be inhabitable. 

[Note. — The presence of clouds indicating both air and 
water ; the regular succession of the seasons, as well as day 
and night ; the suitable amount of light received from the sun ; 
the accompaniment of moons ; the specific gravity of bodies at 
their surface ; all seem to indicate that the primary planets are 
suitable residences for living beings. The only objection to 
this view is, the difference in the amount of heat received from 
the sun, supposing it to be according to the inverse ratio of the 
squares of their distances from the sun. But we see from the 
difference of temperature on the earth, at the base and summit 
of high mountains, that the actual heat depends much upon the 
modifying circumstances, as well as upon the direct rays of the 
sun. And we have reason to suppose that the temperature of 
the other planets does not differ much from that of the earth. 

For instance, the temperature of Mars, as indicated by the 
melting of its snow, and that of Jupiter and Saturn, as indicated 
by the amount of vapor in their atmosphere, appear to be simi- 
lar to that of the earth. Mercury and Venus are protected from 
the direct rays of the sun by dense clouds. Causes unknown 
to us may, and probably do, modify the temperature of all the 
planets in a greater or less degree, sufficiently so, for the pur- 
poses of animal life.] 



LESSON XXX. 

MOON. 
Question. What is the moon? 

Answer. The moon is a secondary planet, re- 
volving round the earth. „ 

Q. Is the moon larger or smaller than the earth ? 

A. It is 49 times less than the earth. 



ILLUSTRATED ASTRONOMY. 43 

Q. What is the diameter of the moon ? 

A. 2,180 miles. 

Q. What is the specific gravity of the moon? 

A. It is 3h times the weight of water, (3.37.) 

Q. What is its mean distance from the earth ? 

A. Two hundred and forty thousand miles. 

Q. In what time does the moon revolve around the earth ? 

A. In about 27 1 days, (27d. 7h. 43m. lis. 5.) 

Q. In what time does the moon revolve upon its axis ? 

A. In about 27h days, or in the same time that 
it revolves around the earth. 

Q. What is the result of the moon's revolving upon its axis 
and around the earth in the same time 1 

A. The same side of the moon is always pre- 
sented to the earth. 

Q. Have we ever seen the opposite side of the moon ? 

A. We have not. 

Q. What causes the moon always to present the same side 
to the earth 1 

A. It is supposed that one side of the moon 
is more dense than the other, consequently the 
centre of gravity is not in the centre of the 
moon. • 

Q. What is a lunation, or lunar month ? 

A. It is the time from one new moon to 
another. 

Q. What is the length of a lunation ? 

A. About 29h days. (29d. 12h. 44m.) 

Q. Why is a lunation longer than the time it takes the moon 
to revolve round the earth ? 

A. Because the earth is revolving around the 
sun at the same time. 



44 ABRIDGMENT OF SMITH'S 



LESSON XXXI. 

Question. What is the length of the days or nights at the 
moon ? • 

Answer. About 15 of our days. 

Q. Which way does the moon revolve around the earth ? 

A. From west to east. 

Q. If the moon revolves from west to east, what causes it to 
rise in the east? 

A. It is caused by the earth's revolving on its 
axis the same way. 

Q. Does the moon rise the same hour every evening? 

A. It rises about 50 minutes later every day. 

Q. What is the cause of its rising 50 minutes later everj 
day? 

A. It is caused by the moon's daily progress in 
its orbit from west to east. 

Q. What causes the phases of the moon, from new moon to 
new moon again ? 

A. It is caused by the moon's revolving around 
the earth. 

Q. When is it new moon ? 

A. When the moon is between the earth and 
sun, and the dark side is presented to us. 

Q. When is it full moon ? 

A. When the moon is upon the opposite side of 
the earth from the sun, and the illuminated side 
is presented to us. 

Q. How much greater is the light of the sun than that of 
the full moon ? 
A. 300,000 times greater. 

Q. When are the sun and moon in quadrature? 

A. When they are ninety degrees distant from 
each other. 



PHASES OF THE MOON. 



NEW,' ! 
MOONvl, 



LAST QUARTER 



FIRST QUARTER 

TELESCOPIC APPEARANCE OF 
THEMOON WHEN 5DAYS OLD. 






ILLUSTRATED ASTRONOMY. 45 

Q. How much of the illuminated side of the moon is visible 
to us when it is in quadrature ? 

A. One-half. 

Q. How much larger is the sun than the moon ? 

A. 70 millions of times greater. 

Q. Why does the moon appear as large as the sun ? 

A. Because it is four hundred times nearer to us 
than the sun. 



LESSON XXXII. 

Question, Has the moon an atmosphere ? 

Ansvjer. Very little, if any. 

Q. What is the appearance of the moon, when viewed with 
a telescope ? 

A. It appears covered with light and dark spots 
of various shapes. 

Q. What is the cause of this appearance? 

A. It is caused by the mountains, plains and 
valleys in the moon. 

Q. What are the light spots ? 

A. Mountains and elevated land. 

Q. What are the dark spots ? 

A. Plains, valleys, &c. 

Q. Has the moon any ocean, seas, or large bodies of water? 

A. Not upon the side towards the earth. 

Q. If you were living upon this side of the moon, what would 
be the appearance of the earth ? 

A. The earth would appear like a large station- 
ary moon. 

Q. How much larger than the moon appears to us ? 
A. Thirteen times greater. 

Q. In what time would the heavenly bodies appear to revolve 
around the moon ? 

A. The stars would appear to revolve in 27^ 
days, the sun in 29s days. 



46 ABRIDGMENT OF SMITH'S 

Q. What is the shape of the moon's orbit? 

A. Elliptical, or one diameter greater than the 
other. 

Q. What is apogee ? 

A. It is the point in the orbit of the moon, far- 
thest from the earth. 

Q. What is perigee ? 

A. It is the point in the orbit of the moon, near- 
est to the earth. 

Q. When is the moon in apogee ? 

A. When it is at its greatest distance from the 
earth. 

Q. When is the moon in perigee ? 

A. When it is nearest to the earth. 

Q. Has the moon any change of seasons ? 

A. None, except those changes which take 
place every lunar month, 

Q. What is the harvest moon ? 

A. When the moon is full in September and 
October, it rises only a few minutes later for sev- 
eral successive evenings, and thus affords light 
for collecting the harvest; it is therefore called 
the harvest moon. 

Q. What is the cause of the harvest moon ? 

A. It is caused by the moon's orbit being very 
oblique to the horizon. 

Q. Is the moon inhabited ? 

A. The want of air and water render it unin 
habitable by beings like ourselves. 



ILLUSTRATED ASTRONOMY. 47 



PHYSICAL CONSTITUTION OF THE MOON. 

In viewing the moon with the naked eye, her disc appears 
diversified with dark and bright spots, which, on being examined 
with a powerful telescope, are discovered to be mountains and 
valleys. The whole surface of the moon is covered with these 
spots, which is evident from the fact that the line of separation 
between the illuminated and dark hemispheres, is at all times 
extremely ragged and uneven. 

The mountains on or near this line cast behind them long 
black shadows, like those of the mountains on the Earth, 
when the sun is rising or setting. The moon is a much more 
mountainous body than the earth, and the mountains are vastly 
higher, compared with its size, than those of the earth. One 
of the mountains, {named Tycho,) situated in the southeast part 
of the Moon, is apparently a volcanic crater 50 miles in diame- 
ter, and 16,000 feet deep, with a central mountain rising to the 
height of 5,000 feet. The height often of the principal moun- 
tains, according to the recent measurement of Maedler, is from 
3^ to 4f miles. The mountains of the moon do not run in 
ranges, like those of the earth ; but are single peaks scattered 
over nearly the whole surface of the moon, and are generally 
of a circular form, shaped like a cup. These facts substan- 
tially prove the mountains of the moon to be of volcanic origin ; 
and in some of the principal ones, decisive marks of volcanic 
stratification, arising from successive deposites of ejected mat- 
ter, may be distinctly traced with powerful telescopes. 

The moon contains no large bodies of water, such as, oceans, 
seas, &c, at least, upon the side visible to us. If there are 
any, they must be upon the opposite side of the moon which is 
never presented to us. The moon also has very little if any 
atmosphere, at least, none of sufficient density to refract the 
rays of light in their passage through it : owing to these two 
circumstances there are no clouds floating around the moon ; if 
there were any, they would at times be visible to us, but none 
have been observed. Ijt presents the sams appearance that it 
did 2,000 years ago ; no trace of vegetation or change of sea- 
sons has been observed ; every thing appears solid, desolate, 
and unfit for the support of animal or vegetable life. 

Whether the materials of which the moon is composed, are 
of the- same nature as the earth, we have no means of knowing. 
It has, however, been ascertained that her density, compared 
with the density of the earth, is .615, or a little more than one 



48 ABRIDGMENT OF SMITH'S 

half; consequently, the materials of which the moon is com- 
posed, are about half as heavy as the same bulk of the earth. 

There being little or no atmosphere about the moon, the 
heavens, during her daytime, have the appearance of night to 
the inhabitants of the moon, when they turn their backs to the 
sun ; and the stars then appear, as bright to them as they do 
in the night to us ; for it is entirely on account of the light 
which our atmosphere reflects, that the heavens appear lumi- 
nous about us in the daytime. If our atmosphere were removed, 
only that part of the heavens would be light, in which the sun 
is situated ; and, if we turned our backs to the sun, the heavens 
would appear as dark as night. 

The light which the full moon affords us is very small, when 
compared with the light of the sun ; it being 300,000 times 
less. It has also been demonstrated, that the light reflected by 
the moon produces no heat ; as its rays, when collected by the 
aid of the most powerful glasses, have not been perceived to 
produce the slightest effect upon the thermometer. 



IS THE MOON INHABITED? 

From the physical constitution of the moon, it is evident that 
the moon is not inhabited ; at least, by beings constituted like 
ourselves. 

The moon having little, or no atmosphere, we could not 
exist upon its surface for a single hour, even though provided 
with the other necessary means for our existence : neverthe- 
less, this is not positive evidence that the moon is not inhabited 
The same power that called the moon into existence, could as 
easily constitute beings fitted to inhabit its surface, and enjoy 
an existence, which is productive of as much happiness to them 
as ours is to us. 

It may be very properly asked — if the moon is not a habita- 
ble body, for what purpose was it created ? This is a question 
which is more easily asked than answered. We might as well 
ask, why the greater portion of the surface of the earth is not 
land instead of water : why is Africa a sandy desert, or why 
are the polar regions unfitted for the habitation of man. 

According to Geologists, the Earth was, for a long period of 
time, in a state unfit for animal life, and that it has undergone 
many successive changes, extending through a long period of 
time, before it was fitted for the abode of mankind. It may be 
that the moon is in a transition state, and has not arrived to a 
state suitable for animal life. 



ILLUSTRATED ASTRONOMY. 49 

We know but few of the numerous purposes the moon may 
serve, in the economy of nature. We do know that it exerts a 
powerful influence in raising the tides. Its mild beams tend to 
dispel the gloom of night, especially in the dreary winter of the 
polar regions. It furnishes, the navigator at sea, the most 
certain means known, of determining his longitude. In the 
earliest periods of the world, its changes furnished the ancients 
with a convenient mode of reckoning time. It is also thought 
by many to exert an important influence upon the animal and 
vegetable kingdoms ; but this is denied by others equally enti- 
tled to credit. 



LESSON XXXIII. 

ECLIPSES. 
Question. What is an eclipse ? 

Answer. It is the interception of the sun's rays 

by some opaque body. 

Q. How are eclipses divided, with respect to the body 
eclipsed ? 

A. Into two kinds, solar and lunar. 
Q. What is a solar eclipse ? 

A. It is an eclipse of the sun. 

Q. What is the cause of an eclipse of the sun ? 

A. It is caused by the moon's passing between 
the earth and sun, and casting its shadow^ upon 
the earth. 

Q. When must an eclipse of the sun take place ? 

A. It can happen only at new moon. 

Q. What is a lunar eclipse ? 

A. It is an eclipse of the moon. 

Q. What causes an eclipse of the moon? 

A. It is caused by the moon's passing through 
the earth's shadow. 

Q- When must an eclipse of the moon take place ? 

A. It can happen only at- full moon. 

5 



50 ABRIDGMENT OF SMITH'S 



Q. How are eclipses divided, with respect to the amou 
eclipsed ? 

A. Into total and partial. 

Q. What is a total eclipse ? 

A. It is an eclipse of the whole of the sun or moon. 

Q. What is a partial eclipse ? 

A. It is an eclipse of only a part of the sun or moon. 

Q. What is an annular eclipse ? 

A. It is an eclipse of the central part of the sun, 
when the moon is so far from the earth, that the 
sun can be seen like a bright ring around it. 

Q. Do we have an eclipse of the sun at every new moon ? 

A. We do not. 

Q. Why do we not have an eclipse of the sun at every new 
moon ? 

A. Because at new moon, the moon is generally 
too high or too low for its shadow to fall upon the 
earth. 

Q. Do we have an eclipse of the moon at every full moon ? 

A. We do not; at full moon the moon generally 
passes above or below the earth's shadow. 

Q. What is the length of the earth's shadow ? 

A. About 600,000 miles. [Note.— This is the 
mean or average length.] 

Q. What is the length of the moon's shadow ? 

A. About 234,000 miles. [Note.— This is the 
mean or average length.] 

Q. What is a digit ? 

A. It is the twelfth part of the apparent diame- 
ter of the sun or moon's disc. 

Q. What is the greatest number of eclipses that can take 
place in a year'? 

A. Seven ; five of tne sun and two of the moon. 

Q. What is the least number of eclipses that can take place 
in a year ? 

A. Two ; and both must be of the sun. 



mt 



ECLIPSES &C. 



EfcRTHS^ 




^^LmiPSEorru 



__ : n^fns shm>° 



Z2Z ~&h PARTIAL ECLIPSE OF THEl 



THE MOONS SHADOW PASSES THE MOON PASSES ABOVET THE 
*BOVE THE NORTH POLE. lAKTMS SHADOW. 



: iwM 



,\?SE o^ 



cGUPSE 



ILLUSTRATED ASTRONOMY. 51 

LESSON XXXIV. 

MOON'S NODES. 

Question. What are nodes ? 

A?iswer. They are two opposite points, where the 
orbit of the moon, or any other planet, intersects 
the plane of the earth's orbit, or ecliptic. 

Q. What*angle does the moon's orbit make with the plane 
of the earth's orbit, or ecliptic. 

A. About 5| degrees. (5° 8' 48".) 

Q. What part of the moon's orbit is above, or north of the 
plane of the earth's orbit ? 

A. One half; the other half being below, or 
south of the earth's orbit. 

Q. What is the ascending node ? 

A. It is that point, where the moon passes the 
plane of the earth's orbit from south to north. 

Q. What is the descending node ? 

A. It is that point, where the moon passes the 
plane of the earth's orbit from north to south. 

Q. Do the nodes change their position, as regards a fixed 
point in the heavens ? 

A. They have a retrograde motion of about 19 
degrees in a year. 

Q. When is the moon in north latitude in the heavens ? 

A. When it is north of the earth's orbit, or 
ecliptic. 

Q. When is the moon in south latitude in the heavens ? 

A. When it is south of the earth's orbit, or 
ecliptic. 

Q. What is the greatest latitude of the moon? 

A. 5\ degrees north or south of the earth's orbit 
or ecliptic. 

Q. What is the greatest declination of the moon, or its dis- 
tance north or south of the equinoctial, or equator? 

A. About 28£ degrees. 



52 



LESSON XXXV. 

Question. How near one of the nodes must the moon be, at 
new moon to cause an eclipse of the sun ? 

Answer. Within seventeen degrees. (16° 59".) 

Q. How near one of the nodes must the moon be, at full 
moon, to cause an eclipse of the moon ? 

A. About 12 degrees. (11° 25' 4".) 

Q. If the moon is exactly in one of her nodes at new or full 
moon, what kind of an eclipse will it cause ? 

A. It will cause a great eclipse of the sun, or 
moon. 

Q. What is the extent of the solar ecliptic limit, in which, an 
eclipse of the sun can take place? 

A. Thirty-four degrees, seventeen degrees on 
each side of either node. 

Q. What is the extent of the lunar ecliptic limit, in which, 
an eclipse of the moon can take place? 

A. Twenty-four degrees, twelve on each side 
of either node. 



HELIOCENTRIC AND GEOCENTRIC LATITUDE AND LONGITUDE. 

Q. What is the Heliocentric latitude and longitude of a 
planet ? 

A. It is its latitude and longitude, as seen from 
the sun. 

Q. What is the Geocentric latitude and longitude of a 
planet ? 

A. It is its latitude and longitude, as seen from 
the earth. 

Q. Does a planet, seen from the earth, appear to have the 
same longitude as it would have, if seen from the sun at the 
same time ? 

A. It does not, unless the earth is between the 
sun and planet. 



ILLUSTRATED ASTRONOMY. 53 

LESSON XXXVI. 

TIDES. 

Question. What motion have the earth and moon, besides 
revolving around the sun ? 

Answer. They revolve around their common 
centre of gravity. 

Q. In what part of a straight line, joining their centres, is 
the centre of gravity situated ? 

A. About 3,200 miles from the centre of the 
earth. 

Q. What effect has the centrifugal force upon the water on 
the opposite side of the earth from the moon ? 

A. It causes it to recede from the centre of 
gravity, and to rise on that part of the earth. 

Q. What effect has this upon the shape of the earth ? 

A. Its diameter is lengthened in the line of the 
moon's attraction, and shortened at right angles 
to it. 

Q. What tends to increase this oval shape of the earth ? 

A. The inequality of the attraction of the moon 
at the different sides of the earth. 

[The water upon the side of the earth nearest to the moon, 
is more attracted than the centre of the earth ; the water upon 
the opposite side is less attracted,] 

Q. What effect does the turning of the earth from west to 
east, on its axis, produce on these elevations or tide waves ? 

A. It causes these elevations, or tide waves, to 
pass from east to west around the earth. 
Q. What is tide ? 

A. It is the rising and falling of the waters of 
the ocean. 



54 ABRIDGMENT OP SMITH'S 



. 



Q. How are the tides divided with respect to the rising and 
falling of the water ? 

A. Into flood and ebb. 

Q. What is flood tide ? 

A. It is the rising of the water. 

Q. What term designates the greatest elevatian of the flood 
tide? 

A. High water. 

Q. What is ebb tide ? 

A. It is the falling of the water. 

Q. How often do flood and ebb tide occur ? 

A. Twice in about 25 hours. 

Q. Do the tides rise at the same hour every day ? 

A. They rise about an hour later each day. 

Q. Why do the tides rise later ? 

A. Because the moon passes the meridian about 
an hour later each day. 

Q. What causes the moon to be later at the meridian ? 

A. It is caused by its daily progress eastward in 
its orbit. 

Q. Does the attraction of the sun produce an effect similar 
to that of the moon ? 

A. It tends to raise a tide two-fifths as high. 

Q. When the sun and moon are on the same or opposite 
sides of the earth, what is the effect of their attractive forces ? 

A. They raise a tide equal to the sum of their 
separate tides. 

Question. When they are in quadrature, what is the effect of 
their counteracting forces ? 

A. They raise a tide equal to the difference of 
their tides. 



1 



TIDES. 



^riRST QUARTER 



/% 






^SPRINCTIDE 



V/ SPRINGTIDE 




NEW MOON OR^ 
CONJUNCTION 






LAST QUARTER 



GREATEST TIDES IN THE 
NORTHERN HEMISPHERE 
DURING THE DAY AND LEAST 
DURING THE NIGHT. 



THE MOON VISIBLE IN 
THE NORTH POLAR 
CIRCLE 14 DAYS IN EACH 

, /LUNATION IN THE WIN- 



THE MOON VISIBLE IN THE 
SOUTH POLAR CIRCLE I4DAYS 
IN EACH LUNATION IN THE 
SUMMER. 



.^ QREATEST TIDES 
f IN THE NORTHERN 
HEMISPHERE OUR INC 
THE NIGHT AND LEAST 
DURING THE DAY. 



ILLUSTRATED ASTRONOMY. 55 



LESSON XXXVII. 

Question. How are tides divided, with respect to their com- 
parative height? 

Answer. Into spring, and neap. 

Q. What is spring tide ? 

A. It is the greatest flood and ebb tide. 

Q. What is neap tide ? 

A. It is the least flood and ebb tide. 

Q. What proportion do these tides bear to each other ? 

A. The neap tide is about three-sevenths as 
great as the spring tide. 

Q. When do spring tides occur ? 

A. Twice in each lunar month, at new and full, 
moon. 

Q. When do neap tides occur ? 

A. Twice in each lunar month, at the quarters. 

Q. What effect have the continents upon the tide waves 
when passing round the earth ? 

A. They subject them to great irregularities. 

Q. Which side of the continents have the highest tides, the 
eastern, or the western ? 

A. The eastern side. 

Q. Does the water remain permanently higher on the east 
than on the west side of the continents ? 

A. The gulf of Mexico is 20 feet higher than 
the Pacific Ocean, and the Red Sea is 30 feet 
higher than the Mediterranean. 

Q. Where the tide wave is least obstructed, as in the Pacific 
Ocean, how much behind the moon is it? 

A. It is two or three hours behind it. 

Q. How long after the moon passes the meridian, is it high 
water at New York ] 

A. About 8k hours. 



56 

Q. If the earth were uniformly covered with water, how high 
would the tide rise ? 

A. Not more than two or three feet. (The tide 
at the small islands in the Pacific ocean is usually 

less.) 

Q. What produces the greatest effect in causing high tides ? 

A. The shape of the land, and the position of 
the shores. 

Q. Where are the highest tides in the world ? 

A. In the bay of Fundy. 

Q. What, besides the position of the shores, tends to raise a 
high tide at that place ? 

A. The meeting of the tide wave from the 
North Atlantic ocean, with the main one from 
the South Atlantic. 

Q. How high are the average spring tides at Cumberland, 
near the head of the Bay of Fundy ? 

A. About 71 feet. 

Q. How high are they at Boston ? 

A. About 11 feet. 

Q. At New York ? 
A. About 5 feet. 

Q. At Charleston, South Carolina? 

A. About 6 feet. 

Q. When do we have the highest tides in the northern 
hemisphere ? 

A. During the day time in summer, and during 
the night in the winter. 



ILLUSTRATED ASTRONOMY. 57 

LESSON XXXVIII. 

ORBITS OF THE PLANETS AND COMETS. 
Question, What is the orbit of a primary planet ? 

Answer. It is the path in which it revolves 
around the sun. 

Q. What is the orbit of a secondary planet? 

A. It is the path in which it revolves around its 
primary. 

Q. What is the form of the orbits of all the planets? 

A. Elliptical, or longer one way than the other. 

Q. Are all the orbits elliptical in the same proportion ? 

A. They are not ; some are more elongated 
than others. 

Q. What is the position of the orbits of all the planets? 

A. They extend from west to east in the 
heavens. 

Q. Do the planes of their orbits intersect the ecliptic, or orbit 
of the earth ? 

A. They do, at small angles. 

Q. Do they all intersect the plane of the earth's orbit at one 
point ? 

A. They do not; but intersect it at different 
points. 

Q. Through what point does the plane of the orbit, of every 
primary planet and comet in the solar system, pass ? 

A. Through the centre of the sun. 

Q. Are the planets at nearly the same distance from the sun ? 

A. They are not, but at very different distances. 

Q. Are their orbits all contained within the zodiac ? 

A. They are, except those of a part of the aste- 
roids. 

Q. How wide is the zodiac ? 

A. Sixteen degrees wide : eight degrees on 
each side of the ecliptic. 



58 ABRIDGMENT OF SMITH'S 

Q. Do all the planets revolve around the sun in the same 
direction ? 

A. They do; from west to east. 

Q. Do they all move with the same velocity ? 

A. The velocity decreases as the distance from 
the sun increases. 

Q. Which planet moves in its orbit with the greatest velocity ? 

A. Mercury. 

Q. Which moves with the least ? 

A. Leverrier, or Neptune. 

Q. When does a planet have north latitude ? 

A. When it is above, or north of the earth's 
orbit. 

Q. When does a planet have south latitude ? 

A. When it is below, or south of the earth's orbit. 



LESSON XXXIX. 

COMETS. 
Question. What are comets ? 

Answer. They are bodies which revolve around 
the sun in very elongated orbits. 

Q. How are comets usually distinguished from the planets ? 

A. By a luminous train or tail, on the opposite 
side from the sun. 

Q. Is this luminous train always on the opposite side from 
the sun? 

A. Not always ; a few have been observed to 
have a different direction. 

Q. Do comets ever appear without a luminous train ? 

A. Some are entirely destitute of any such 
appendage. 

Q. What is the number of comets? 

A. The number is not known ; about 500 have 
been seen at different times. 



ILLUSTRATED ASTRONOMY. 59 

Q. Are comets solid bodies like the planets ? 

A. They generally are not ; although some have 
been observed to have a dense nucleus, or head. 

Q. What is the nature of comets ? 

A. They are supposed to be gaseous matter, 
in the form of smoke, fog, or clouds. 

Q. Do comets shine by their own, or by reflected light ! 

A. They shine by rellected light. 

Q. Do they all, like the planets, revolve in the same direc- 
tion around the sun ? 

A. They do not; they revolve in different 
directions. 

Q. Are all their orbits within the zodiac ? 
A. They are not ; their orbits are in all direc- 
tions in the heavens. 

Q. How do many of them move when first seen? 

A. They appear to move in almost a direct line 
towards the sun. 

Q. Does their velocity increase as they approach the sun ! 

A. It does; and when near it, they move with 
immense velocity. 

Q. How fast has a comet been known to move ? 

A. 880,000 miles an hour. 



LESSON XL. 

ATMOSPHERE. 
Question. What is air? 

Answer. It is an elastic, invisible fluid, which 
surrounds the earth. 

Q. Of what, besides air, is the atmosphere composed ? 

A. Of vapor, carbonic acid, and other gases. 

Q. Is the atmosphere of the same density as we ascend from 
the earth 1 

A. It grows thinner or less dense. 




60 ABRIDGMENT OF SMITH J S 

Q. What is the estimated height of the atmosphere? 

A. About forty-five miles. 

Q. What is the pressure of the atmosphere upon the earth? 

A. Nearly fifteen pounds to the square inch. 
(14.6.) 

Q. What is the weight of air compared with water ? 

A. It is 816 times lighter than water. 

Q. The pressure of the atmosphere is equal to the weight of 
a column of water, of what height ? 

A. Thirty-three feet. 

Q. Of what is air composed ? 

A. Of oxygen and nitrogen gases. 

Q. In what proportions ? 

A. Twenty parts of oxygen to eighty parts of 
nitrogen. 



LESSON XLI. 

REFRACTION. 
Question. What is refraction ? 

Answer. It is the deviation of the rays of light 
from a straight line. 

Q. What is astronomical refraction ? 

A. It is the deviation of the rays of light in their 
passage through the atmosphere. 

Q. What is the cause of this refraction? 

A. It is caused by the increase of the density 
of the atmosphere towards the earth. 

Q. In what part of the heavens is the light of a body most 
refracted ? 
A. In the horizon. 

Q. What effect does this refraction have upon the sun at its 
rising and setting ? 

A. It makes the sun appear above the horizon 
when it is actually below it. 



Irefraction, parallax, light *heat 




THE PLANETS INCREASE OR DECREASE >N PRO = 
"PORTION TO THE SPUARE OF THEIR DISTANCES FROM THE SUN 



,^r5rt^"~ 



*RCER THAN A 



ILLUSTRATED ASTRONOMY. 61 

Q. Does this affect the length of the day ? 

A. It makes the day from six to ten minutes 
longer, from sunrise to sunset. 

Q. Is the light of a body refracted when it is in the zenith ? 

A. It is not. 

Q. What is twilight? 

A. It is that faint light, seen before the sun rises 
and after it sets. 

Q. What is the cause of twilight ? 

A. It is caused by the atmosphere's reflecting 
the light of the sun. 

Q. Twilight ceases when the sun is, how far below the 
horizon ? 

A. Eighteen degrees. 



LESSON XLII. 

PARALLAX. 

Question. What is parallax ? 

Answer. It is the difference between the appa- 
rent and true place of a heavenly body. 

Q. What is the apparent place of a planet ? 

A. It is the place where it appears to be, when 
seen from the surface of the earth. 

Q. What is the true place of a planet ? 

A. It is the place where it would appear to 
be, if seen from the centre of the earth, or centre 
of motion. 

Q. Where is the parallax of a heavenly body the greatest ? 

A. At the horizon, and decreases to the zenith. 

Q. How are parallaxes divided? 

A. They are divided into two kinds, diurnal 
and annual parallax. 

Q. What is diurnal parallax ? 

A. It is the apparent difference in the situation 

6 



62 



ABRIDGMENT OF SMITHS 



of a heavenly body, when seen in the zenith and 
horizon of two places, at the same time. (See 
parallax of Mars and Moon.) 

Q. What is annual parallax? 

A. It is the apparent difference in the situation 

of a star, as seen from the earth in opposite points 

of its orbit. 

Q. Have the stars been observed to have any sensible 
parallax ? 

A. A few have been observed to have a small 
parallax of a part of a second. (Note.-^No paral- 
lax has been discovered in more than 30 or 40 of 
them.) 

Q. What is the cause of their having no appreciable parallax ? 

A. Because they are at such an immense dis- 
tance from us. 

Q. If the earth's orbit were a solid ring, how large would it 
appear when viewed from the nearest fixed star ? 

A. No larger than a lady's finger ring. 



LESSON XLIII. 

LIGHT AND HEAT. 
Question. What bodies produce light? 

Answer. Luminous bodies. 

Q. Is light a substance thrown off from a luminous body, or 
is it caused by a vibratory motion ? 

A. It is probably caused by the undulations of 
an extremely subtle fluid. 

Q. In what direction are the rays of light thrown off from a 
luminous body ? 

A. In straight lines, and in all directions. 

Q. With what velocity does light move ? 

A. About 192,000 miles a second. (192,500.) 



ILLUSTRATED ASTRONOMY. 63 

Q. How was this amazing velocity ascertained ? 

A. By observing the eclipses of Jupiter's moons. 

Q. In what proportion do the light and heat of the planets 
increase or decrease ? 

A. In inverse proportion to the squares of their 

distances from the sun. 

Q. Which planet has the most light and heat, and which the 
least ? 

A. Mercury has the most, and Leverrier the 
least. 

Q. If a board a foot square be placed one foot from a lighted 
candle, how many feet square would the shadow be upon the 
wall, nine feet from the candle ? 

A. Nine feet square, or eighty one square feet. 

Q. What amount of light and heat would fall upon the one 
foot and upon the 81 feet? 

A. The same amount of light and heat would 
fall upon each. 



LESSON XLIV. 

TERRESTRIAL AND CELESTIAL GLOBES. 
Question. What is a globe ? 

Answer. A globe is a round body or sphere. 

Q. How many kinds of globes are there used in Astronomy ? 
A. Two; terrestrial and celestial globes. 

Q. What does the terrestrial globe represent? 

A. It represents the earth. 

Q. What are drawn upon the surface of the terrestrial globe ? 

A. Continents, islands, mountains, oceans, seas, 
rivers, republics, kingdoms, empires, &c. 

Q. What does the celestial globe represent ? 

A. It represents the heavens as seen from the 
earth. 

Q. What are usually drawn on the celestial globe ? 

A. The constellations or stars, galaxy or milky 



64 ABRIDGMENT OF SMITH'S 

way, and the figures of various animals and 
objects from which the constellations are named. 

Q. What is a constellation ? 

A. It is a group of stars, to which is applied the 
name of some animal or object. 

Q. What is the number of constellations ? 
A. Ninety-three. 

Q. In viewing the terrestrial globe, where is the observer 
supposed to be placed ? 

A. On its surface. 

Q. In viewing the celestial globe, where must the observer 
suppose himself to be placed ? 

A. In the centre, looking towards the heavens. 
(Inside, looking out.) 

Q. What is the galaxy or milky way ? 

A. It is a luminous belt forming a complete cir- 
cle in the heavens. 

Q. Of what is the galaxy or milky way composed ? 

A. It is a vast number of stars, so far distant 
from us, and situated so nearly in the same direc- 
tion, as to appear like a thin cloud. 

Q. What is the position of the milky way in the heavens ? 

A. It extends from northeast to southwest 
through the whole circumference of the hea 
vens. 

Q. What are the celestial poles, or poles of the heavens? 

A. They are the points where the earth's axis, 
if extended, would meet the heavens. 



II 




ILLUSTRATED ASTRONOMY. 65 



LESSON XLV. 

Question. What does the plane of the equator form, when 
extended to the heavens ? 

Answer. The equinoctial, or celestial equator. 

Q. At what angle do the ecliptic and equinoctial intersect 
each other ? 

A. At an angle of 23^ degrees. (23° 28'.) 

Q. What does the plane of a meridian form, when extended 
to the heavens ? 

A. A celestial meridian, or circle of declination. 

Q. What are measured on celestial meridians ? 

A. Declination and polar distance. 

Q. What is the declination of a heavenly body? 

A. It is its distance from the equinoctial, north 
or south. 

Q. To what are the declination and polar distance always 

equal ? 

A. They are equal to 90 degrees, or a quarter 
of a circle. 

Q. What is the right ascension of a heavenly body? 

A. It is its distance east of the first point of 
Aries, measured on the equinoctial. 

[Q. What angle expresses the right ascension 1 

A. The angle between the meridian passing through the 
body, and the one passing through the first point of Aries.] 

Q. How far is right ascension reckoned ? 

A. 360 degrees, or quite round the heavens. 

Q. What are circles of latitude on the celestial globe ? 

A. They are great circles which pass through 
the poles of the ecliptic, and cut its plane at right 
angles. 

Q. What is the latitude of a heavenly body ? 

A. It is its distance north or south of the eclip- 
tic, measured on a circle of celestial latitude. 



66 ABRIDGMENT OF SMITH'S 

Q. What is the longitude of a heavenly body ? 

A. It is its distance east of the first point of 
Aries, measured on the ecliptic. 

[Q. What angle expresses the longitude 1 

A. The angle between the circle of latitude passing through 
the body, and the one passing through the first point of Aries. 
Q. Where is this angle formed % 

A. At the poles of the ecliptic, where the circles of latitude 
intersect each other.] 

Q. How far is celestial longitude reckoned ? 

A. It is reckoned 360 degrees. 



LESSON XLVI. 

Question. What is a vertical circle ? 

Afiswer. It is a great circle in the heavens, pass- 
ing through the zenith and nadir, and cutting the 
horizon at right angles. 

Q. What vertical circle is the meridian ? 

A. It is that vertical circle which passes through 
the north and south points of the horizon. 

Q. Which is the prime vertical ? 

A. The vertical circle which passes through the 
east and west points of the horizon. 
Q. What are measured on the vertical circles ? 

A. Altitude and zenith distance. 

Q. What is the zenith distance of a heavenly body? 

A. It is its distance from the zenith. 

Q. To what are the altitude and zenith distance always equal ? 

A. They are equal to 90 degrees. 

Q. What is the azimuth of a heavenly body ? 

A. It is its distance east or west of the meri- 
dian. 

[Q. What angle expresses the azimuth *? 

A. The angle between the meridian and the vertical circle 
passing through the body. 



ILLUSTRATED ASTROXOMY. 67 

Q. What is the amplitude of a heavenly body 1 
A. It is its distance north or south of the prime vertical. 

Q. "What angle expresses the amplitude 1 

A. The angle between the prime vertical, and the vertical 
circle passing through the body. 

Q. Where are the angles expressing azimuth and amplitude formed 1 
A. At the zenith where the vertical circles intersect each 
other. 

Q. On what circle are these angles measured ! 
A. On the horizon. 

Q. To what are azimuth and amplitude always equal 1 
A. They are equal to 90 degrees.] 

[The diagram can be used to illustrate azimuth, amplitude, altitude, and 
zenith distance, by supposing the ecliptic to represent the celestial horizon, 
and the circles of celestial latitude to represent vertical circles.] 



LESSON XLVII. 

THE FIXED STARS. 

Question. What are those stars called which always appear 
to be in the same situation with respect to each other ? 

Answer. They are called the fixed stars. 
Q. What are the fixed stars supposed to be ? 

A. They are supposed to be suns like our own, 
with planets revolving around them. 

Q. Are the stars luminous or opaque bodies ? 

A. They are luminous bodies. (Astronomers 
have no doubt on this point.) 

Q. Are all the stars of the same magnitude as the sun ? 
A. They are not ; some are larger, and others 
no doubt smaller than the sun. 

[Astronomers, until recently, considered all the stars to be of about the 
same magnitude, and probably as large as the sun ; and that the stars of the 
first magnitude owed their brilliancy to their being nearer to us ; but it has 
been found that the brightest star (Sirius) in the whole heavens, and which 
was considered to be the nearest fixed star, is at a much greater distance 
than some of the smaller stars. This clearly demonstrates that they are of 
very unequal magnitude.] 



63 ABRIDGMENT OF SMITH'S 

Q. What is the distance of the nearest fixed star, a (Alpha) 
Centauri ? 

A. It is so far distant that a cannon ball going 
500 miles an hour, would take four millions of 
years to reach it. 

Q. What is the number of stars whose distance is imperfectly 
known to us ? 

A. At>out 35 ; seven of which have their dis- 
tances determined with considerable certainty. 

Q. Do all the stars remain of the same brilliancy? 

A. They do not ; some exhibit a periodical 
change in their light. 

Q. What is supposed to be the cause of this change in their 
light? 

A. The revolution on their axes is supposed to 
present, alternately to us/ sides of different bright- 
ness. 

Q. What are those stars called, which appear to be sur- 
rounded by a thin atmosphere ? 

A. Nebulous stars. 

Q. Do stars ever disappear, or new ones become visible ? 
A. Thirteen stars have disappeared, and ten 
new ones become visible, during the last century. 

[There are now seven or eight well-attested cases of fixed stars suddenly 
glowing for a time with such brilliancy as to be visible in the day time, 
through the intensity of their light ; then gradually fading away, and becom- 
ing entirely extinct. Laplace thinks that some great conflagrations, pro- 
duced by extraordinary causes, have taken place on their surface. 

Q. What is supposed to be the cause of their disappearance ? 

A. They have probably ceased to be luminous. 

Q. How do astronomers account for the appearance of new 
stars ? 

A. Opaque bodies may have become luminous, 
or new suns may have been created. 



BINARY ORDOUBLE STARS 

THESE STARS REVOLVE AROUND A COMMON CENTRE OF GRAVITY BE - 
-TWEEN THEM, AND APPEAR SINGLE UNLESS vrEWED THROUGH A 
GOOD TELESCOPE. 



CASTOR CORONA RICEL 



LION NORTH STAR 



LEONIS POLARIS 







ILLUSTRATED ASTRONOMY. 69 



LESSON XLVIII. 

Question. What do the milky way and the single stars that 
are visible to the naked eye, including our sun, constitute ? 

Answer. They constitute an immense cluster, or 
firmament, entirely distinct from the other clus- 
ters or nebulae of the heavens. 

Q. What is the shape of this great cluster or firmament ? 

A. It has the form of a wheel or burning-glass. 

[The stars extend much farther in the direction of the plane of the milky 
way, than they do at right angles to it.- See Diagram.] 

Q. W T hat is the number of stars in our cluster ? 

A. They have been variously estimated, from 
10 to 100 millions. 

Q. By what term do some astronomers designate our cluster 
or firmament ? 

A. They call it the universe. 

[The term universe, was until recently a used to denote the whole creation 
of God, and was never used in the plural number; but astronomers use the 
term to denote an immense firmament or cluster of stars, entirely distinct 
from other clusters— of W.EL&3 mere are many tnousands visible with the tele- 
scope—and are at an immense distance from each other. Hence, in speaking 
of these clusters, they call them universes. — Prof. Mitchell.] 

Q. Do the fixed stars have any apparent motion ? 

A. They do, but it is so slight as not to be 
easily detected. 

Q. Around what, are all the stars in our cluster, including 
the sun, supposed to revolve ? 

A. Around the common centre of gravity of the 
cluster. 

Q. What group of stars is thought to be near the centre 
of the cluster? 

A. The Pleiades, or seven stars. — (Dr. Maed- 
ler.) 



70 ABRIDGMENT OF SMITHES 

Q. In what part of the cluster is the solar system situated? 

A. It is comparatively near the centre. 

Q. How far from us is the centre of the cluster supposed 
to be ? 

A. About 150 times the distance of the nearest 
fixed star. 

[Light is about 8 minutes in coming from the sun ; about 
3 J years in coming from the nearest fixed star, a Centauri; 
about 500 years in coming from the supposed centre of the 
cluster ; and about 5,000 years in coming from the most remote 
stars in the cluster.] 

Q. How long will it take the sun to revolve around this cen- 
tre of gravity 1 

A. About twelve millions of years. 

Q. What other motion have some of the stars, besides around 
the centre of the cluster? 

A. Multiple stars, consisting of two or more, 
revolve likewise around their common centre of 
gravity. 

Q. What is the number of these multiple stars ? 

A. About 6,000 have been observed. 

Q. Do these stars appear double to the naked eye .? 

A. They do not ; the most, require a good tele- 
scope to separate them. 

Q. When multiple stars consist of but two, what are they 
usually called ? 

A. Double stars, or binary systems. 



LESSON XLIX. 

NEBULH. 
Question. What appearance has a nebula ? 

Answer. A nebula appears like a spot of pale 
light seen in the heavens. 

Q. Of what are the nebulae composed ? 

A. The most of them are great clusters of 



ILLUSTRATED ASTRONOMY. 71 

stars, so far distant as to appear like a thin 
cloud. 

Q. Are there many of them ? 

A. About 6,000 have been discovered. 

[Note. — Their number is probably much greater; perhaps infinite.] 
Q. What is the distance of these nebulae ? 

A. Some of them are said to be so far distant, 
that light, travelling 192 thousand miles a second, 
would not reach us in less than 30 millions of 
years. — [Prof. Mitchell.] 

Q. Are they visible to the naked eye ? 

A. Only a few are seen without a telescope. 

Q. How large do they appear when viewed with a telescope ? 
A. Some of them appear as large as one-tenth 
of the disc of the moon. 

Q. Are these nebulas seen in all parts of the heavens ? 

A. They are, although they are more numerous 
in a narrow zone, circumscribing the heavens, at 
right angles to the milky war. 

Q. Into how many classes may neouise be divided ? 

A. Into five classes; viz., resolved nebulae, re- 
solvable nebulae, stellar nebulae, irresolvable and 
planetary nebuhe. 

Q. What are resolved nebulae ? 

A. They are those, which nave oeen discovered 
with the telescope to be great clusters of stars. 

Q. What are resolvable nebulae ? 

A. They are those, which are considered to be 
composed of stars, but are so far distant that the 
telescopes have not as yet resolved them. 

Q. What are stellar nebulae ? 

A. They are those of an oval or round shape, 
increasing in density towards the centre. 

[Note.— They sometimes present the appearance of having a dim star in 
th* centre l 



72 ABRIDGMENT OF SMITH'S 

Q. What are irresolvable nebulae ? 

A. They are those/which are considered to be 
luminous matter in an atmospheric state, con- 
densing into solid bodies like the sun and planets, 

Q. What are the planetary nebulae? 

A. They are those, which resemble the disc of a 
planet, and are considered to be in an uncon- 
densed state. 

Q. Are all nebulae beyond our cluster ? 

A. They are, except the milky way, and nebu- 
lous stars. 

Q. By what general term do astronomers designate each 
nebula or cluster ? 

A. They call each nebula a Universe, or Fir- 
mament. 

[ Q. "What can you say of the great nebula in the Greyhounds 1 
A. It resembles our own cluster, or firmament of stars. 
Q. What can you say of the great nebula in Orion 1 
A. This nebula was considered to be luminous matter in a.n 

uncondensed state; but it has lately been discovered to be star* 

by Lord Rosse, with his powerful telescope. 

Note.— This nebula is visible to the naked eye. 

Q. What is the probable cause of many of the nebulae appearing elliptical 
or elongated! (See Diagram.) 

A. It is probably caused by the edge of the nebula bein*; 
turned more or less towards us.] 




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